Hengshan Mts, Shanxi, is located in the ecotone between temperate grassland zone and warm-temperate deciduous broad-leaved forest zone according to the result of China vegetation regionalization. The differences between vegetation types on the south and north slopes of Hengshan Mountains were studied comparatively by using both TWINSPAN and DCA based on the vegetation data set from the field. The result produced by TWINSPAN indicated that the vegetation was divided into 16 and 20 associations, among which Ass. Larix principis-ruprechtii_Dendranthema chanetii, Ass. Larix principis-ruprechtii_Hippophae rhamnoides subsp.sinensis_Sanguisorba officinalis, Ass. Larix principis-ruprechtii_Equisetum ramosissmum, Ass. Roegneria kamoji+Sanguisorba alpine, Ass. Larix principis-ruprechtii_Potentilla anserine, Ass. Larix principis-ruprechtii_Calamagrostis pseudophragmite, Ass. Artemisia brachyloba+Dendranthema chanetii, Ass. Leymus secalinus+Artemisia brachyloba, Ass. Ostryopsis davidiana_Carex lanceolata, Ass. Spiraea trilobata_Artemisia brachyloba+Leymus secalinus, Ass. Spiraea trilobata_Artemisia brachyloba_Dendranthema chanetii+Dendranthema chanetii, Ass. Artemisia brachyloba+Oxyktropis caerulea, Ass. Carex lanceolata, Ass. Artemisia brachyloba+Artemisia lavandulaefolia, Ass. Artemisia brachyloba, and Ass. Artemisia giraldiir +Artemisia brachyloba on the south slope and belonged to 6 formations, moreover, Ass. Stipa bungeana, Ass. Puccinellia distans+Senecioneae sp., Ass. Poa sphondylodes+ Carex lanceolata, Ass. Senecioneae sp. +Siline jenisseensis, Ass. Sanguisorba alpina+Artemisia lavandulaefolia, Ass. Siline jenisseensis-Artemisia lavandulaefolia, Ass. Denfranthema zawwadskii+Artemisia lavandulaefolia, Ass.Denfranthema zawwadskii+Poa sphondylodes, Ass. Populus cathayana, Ass. Carex lanceolata+Anaphalis hancockii, Ass. Larix principis-ruprechtii_Poa sphondylodes, Ass. Larix principis-ruprechtii_Carex lanceolata, Ass. Larix principis-ruprechtii_Polygonum viviparum, Ass. Larix principis-ruprechtii_Equisetum ramosissmum, Ass. Larix principis-ruprechtii_Hippophae rhamnoides subsp.sinensis_Roegneria kamoji, Ass. Carex lanceolata+Poa sphondylodes+Sanguisorba alpine, Ass. Sanguisorba alpina+Galium verum, Ass. Artemisia brachyloba+Artemisia lavandulaefolia, Ass. Spiraea trilobata_Poa sphondylodes, and Ass. Hippophae rhamnoides subsp. sinensis_Viicia amoena on the north slope belonging to 11 formations.
The result produced by DCA showed that vegetation of the south slope varies from Artemisia brachyloba scrub arid-tolerance to cold-temperature coniferous forest and that of the north slope varies e.g, Stipa bungeana steppe to cold-temperature coniferous forest along first axis standing for elevation and temperature. Down the second axis standing for moisture, south slope varies from Ass. Artemisia brachyloba at low elevation to Ass. Larix principis-ruprechtii at high elevation, while the north slope varies from Ass. Stipa bungeana and Ass. Puccinellia distans to Ass. Populus cathayana. The result from the ordination suggested some substantial differences concerning vegetation types of both slopes, namely, Ass. Spiraea trilobata, Ass. Spiraea trilobata_Artemisia brachyloba+Leymus secalinus, and Ass. Ostryopsis davidiana_Carex lanceolata were the secondary vegetations after deciduous broad-leaved forest was destroyed in the south slope，while Ass. Stipa bungeana, Ass. Puccinellia distans+Senecioneae sp., Ass. Spiraea trilobata_Poa sphondylodes, and Ass. Denfranthema zawwadskii+Poa sphondylodes in the north slope had characteristics typical of steppe vegetation. With the rising of elevation, the vegetation types showed some homogeneity.
Compared between vegetation types including Form. Larix principis-ruprechtii, Form. Artemisia brachyloba, Form. Spiraea trilobata, Form. Ostryopsis davidiana, Form. Hippophae rhamnoides subsp.sinensis, Form. Carex lanceolata, Form. Stipa bungeana, Form. Senecioneae sp., Form. Poa sphondylodes, Form. Artemisia lavandulaefolia, Form. Populus cathayana, Form. Sanguisorba alpine, and Form. Hippophae rhamnoides subsp. sinensis in the south and north slopes, it showed that they shared Form. Larix principis-ruprechtii, Form. Artemisia brachyloba, Form. Spiraea trilobata, and Form. Carex lanceolata in both the slopes. However, some obvious difference existed in association numbers. The association number of Form. Spiraea trilobata and Form. Artemisia brachyloba on the south slope were more than those on the north slope, and the association number within Form. Carex lanceolata was more on the north slope than on the south, while the association number of Form. Larix principis-ruprechtii was close on both the slopes. All above differences were closely related to different vegetation zones with different collocations of ecological factors on different slopes such as water and temperature.